Use this one; it is good.
http://www.hamline.edu/~arundquist/equationeditor/

This one is ugly, but you'll live.
<A href="http://www.atp.ruhr-uni-bochum.de/VCLab/software/HotEqn/HotEqn.html">http://www.atp.ruhr-uni-bochum.de/VCLab/software/HotEqn/HotEqn.html</A>